One of the cornerstones of Charles Darwin’s theory of Natural Selection is that adaptation to environmental characteristics will accelerate the creation of new species. Direct evidence for this has been found in support for this idea, according to an article published in the open-access journal PLoS ONE on April 2, 2008.
The process of speciation involves the separation of one population into more than one group of similar but notably different populations. While there are many definitions for the minimal separation necessary for speciation, it is often defined by the ability of the two groups to produce fertile young, and is generally accepted that phenotypic and genotypic divergence increases the chances of this.
“A single adaptive trait such as color could move a population towards the process of forming a new species, but adaptation in many traits may be required to actually complete the formation of an entirely new species,” says co-author Patrik Nosil, a post-doctoral fellow at the University of British Columbia. “The more ways a population can adapt to its unique surroundings, the more likely it will ultimately diverge into a separate species.”
For the first time, an experiment has been conducted in nature to examine this. The group studied walking-stick insects in the Santa Barbara Chaparral in southern California. Stick insects cannot fly and feed on their respective host plants. There are several distinct “eco-types” of walking-sticks that are found on different types of plants and with different color patterns to match their hosts. For instance, the cristinae ecotype specifies insects with a white line along their green bodies, which helps them to resemble their host plants, which have needle-like leaves. Photos of different eco-types and their host plants are available at the following URL: http://www.publicaffairs.ubc.ca/download.
In this field experiment, the team displaced some eco-types from their customary host plants, while protecting some others from their natural predators. The sticks were then analyzed genotypically and phenotypically to determine how divergent their traits had become in the experimental period.
It was found that even color pattern alone could initiate the process of speciation. Natural selection on different traits, such as an ability to detoxify host-plant chemicals, are also necessary to continue the speciation process that is initiated by such traits as color pattern.
Nosil believes that this is further strong evidence for Darwin’s famous theory, displayed in a different setting and with different evolutionary pressures from previous studies. “Natural selection has been widely regarded as the cause of adaptation within existing species while genetics and geography have been the focus of most current research on the driving force of speciation,” he says. “As far as advancing Darwin’s theory that natural selection is a key driver of speciation, this is the first experiment of its kind done outside of a lab setting. The findings are exciting.”
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Ecological Niche Dimensionality and the Evolutionary Diversification of Stick Insects.
Nosil P, Sandoval CP
PLoS ONE 3(4): e1907.
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Written by Anna Sophia McKenney